Methods for reading data from a storage medium using a reader and storage devices

ABSTRACT

According to various embodiments, a method for reading data from a storage medium using a reader may be provided. The method may include: reading a first signal with a reader head of the reader at a first position of the storage medium; reading a second signal with a reader head of the reader at a second position of the storage medium; and determining data stored at a pre-determined position of the storage medium based on the first signal and based on the second signal.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of the U.S. provisionalpatent application No. 61/671,832 filed on Jul. 16, 2012, the entirecontents of which are incorporated herein by reference for all purposes.

TECHNICAL FIELD

Embodiments relate generally to methods for reading data from a storagemedium using a reader head and to storage devices.

BACKGROUND

The amount of data to be stored on data storage devices is increasing.Thus, it may be desired to provide data storage devices with a high datastorage capacity.

SUMMARY

According to various embodiments, a method for reading data from astorage medium using a reader (with one reader head or with a plurality(for example an array) of reader heads, for example multiple readers ona single slider) may be provided. The method may include: reading afirst signal with a reader head of the reader at a first position of thestorage medium; reading a second signal with a reader head of the readerat a second position of the storage medium; and determining data storedat a pre-determined position of the storage medium based on the firstsignal and based on the second signal. The reading of the signal can besequential (for example using a single reader head) or parallel (forexample using multiple reader heads in a slider).

According to various embodiments, a storage device may be provided. Thestorage device may include: a storage medium; a reader (for exampleincluding one reader head or multiple reader heads; in other words: aplurality of read heads) configured to read a first signal with a readerhead of the reader at a first position of the storage medium andconfigured to read a second signal with a reader head of the reader at asecond position of the storage medium; and a data determination circuitconfigured to determine data stored at a pre-determined position of thestorage medium based on the first signal and based on the second signal.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments are described with reference to the following drawings, inwhich:

FIG. 1A shows a flow diagram illustrating a method for reading data froma storage medium using a reader (with one reader header or with aplurality of reader heads) in accordance with an embodiment;

FIG. 1B shows a storage device in accordance with an embodiment;

FIG. 2 shows a schematic illustration of a wide reader for shingledtracks on a recording medium in accordance with an embodiment;

FIG. 3 shows an illustration of a de-convolution method for afixed-offset adjacent track subtraction method in accordance with anembodiment;

FIG. 4 shows a diagram of simulated shingle write pattern in accordancewith an embodiment;

FIG. 5 shows a simulated read back from a reader which is wider than thetrack pitch in accordance with an embodiment;

FIG. 6 shows an illustration of signal processing of a fixed-offsetadjacent track subtraction method on simulated signal in accordance withan embodiment;

FIG. 7 shows an illustration of recovered simulated written signal inaccordance with an embodiment;

FIG. 8 shows an illustration of a read back signal X₁ and X₂ over 2shingle tracks in accordance with an embodiment;

FIG. 9 shows an illustration of a general schematic diagram ofdeconvolution based on amplitude coefficient estimation method inaccordance with an embodiment;

FIG. 10 shows an illustration of a schematic diagram of deconvolutionbased on amplitude coefficient estimation method in sequential pluralityreading in accordance with an embodiment;

FIG. 11 shows an illustration of a first phase and amplitude coefficientdetector scheme implementing a cross-correlation method or matchingfilter method;

FIG. 12 shows an illustration of an extraction of continuous PES signalsout from high sampling amplitude coefficient;

FIG. 13 shows a dual stage PES Servo configuration;

FIG. 14 shows a second phase and amplitude coefficient scheme includinga preamble as phase synchronization and introducing an additionalmulti-frequency data pattern in data region for amplitude coefficientdetection;

FIG. 15 shows a diagram and a signal associated to the second scheme;

FIG. 16 shows a signal comparison between original track signal andreconstructed track signal;

FIG. 17 shows a SNR comparison for the case NR (No signal recoveryapply), 1 and 2 (shingle track signal recovered using the scheme 2),NT31 (original shingle track with no adjacent interference) and WT31(wide track signal);

FIG. 18 shows a third phase and amplitude coefficient detection schemewherein a buried layer dedicated servo can generate both PES and phasesynchronization signal for wide reader magnetic recording; and

FIG. 19 shows an illustration of a writing scheme for wide reader inshingle magnetic recording in accordance with an embodiment;

FIG. 20 illustrates a system for real time spindle speed variation andrelative head-disk motion measurement in accordance with a presentembodiment:

FIG. 21 illustrates a double filter variant of the system of FIG. 20 inaccordance with the present embodiment:

FIG. 22 illustrates a graph of filtered signals of the variant system ofFIG. 21 in accordance with the present embodiment;

FIG. 23, comprising FIGS. 23A, 23B, 23C, and 23D, illustratesexperimental results from the system of FIG. 20 in accordance with thepresent invention, wherein FIGS. 23A and 23B show experimental resultsobtained using the system of FIG. 20 on an air bearing spindle with ameasured spindle speed variation and FIGS. 23C and 23D show experimentalresults obtained using the system of FIG. 20 for measurements on a harddisk drive (HDD) product;

FIGS. 24A and 24B illustrate experimental results obtained using thesystem of FIG. 21 for measurements on the HDD product of FIGS. 23C and23D in accordance with the present invention;

FIG. 25 illustrates a cutaway view of a read-write head over disk mediain accordance with the present invention;

FIG. 26 illustrates a top planar view of the reader head of FIG. 25superimposed over tracks of a servo layer of the disk media of FIG. 25in accordance with the present embodiment;

FIG. 27, comprising FIGS. 27A and 27B, illustrates block diagrams ofsynchronization signal generation and processing for detection ofdowntrack vibration, spindle speed variation and jitter in accordancewith the present embodiment, wherein FIG. 27A depicts a block diagram ofthe synchronization signal generation and FIG. 27B depicts a blockdiagram of the synchronization signal processing;

FIGS. 28A and 28B illustrate a first set of simulation results of thesynchronization signal processing of FIG. 27B in accordance with thepresent embodiment;

FIG. 29 illustrates a second set of simulation results of thesynchronization signal processing of FIG. 27B in accordance with thepresent embodiment;

FIG. 30 illustrates spinstand simulation results of the synchronizationsignal processing of FIG. 27B in accordance with the present embodiment;

FIG. 31 illustrates a graph of a normal synchronization signal and adetected synchronization signal in a speed increase situation inaccordance with the present invention;

FIG. 32 illustrates a block diagram of position error signal (PES)generation and flying height signal generation in accordance with thepresent invention;

FIG. 33 illustrates Wallace equation generation in accordance with thepresent embodiment;

FIG. 34, comprising FIGS. 34A and 34B, illustrates a graph of touchdowncurves in accordance with the present embodiment, wherein FIG. 34Adepicts a touchdown curve using flying height signals averaged over onehundred measurements and FIG. 34B depicts a touchdown curve using aninstantaneous flying height signal measurement;

FIG. 35 illustrates a graph of experimental results for off-trackvariations of the flying height signal measured in accordance with thepresent embodiment;

FIG. 36, comprising FIGS. 36A and 36B, illustrates simulation results offlying height signals under various conditions in accordance with thepresent embodiment wherein FIG. 36A depicts the flying height signalvibration prior and acoustic emissions (AEs) and FIG. 36B depicts rootmean square values of the flying height signal as well as AE sensorsignals;

FIG. 37 illustrates a graph of a change in the flying height signal fromthermal flying height control (TFC) actuation at different altitudes inaccordance with the present embodiment; and

FIG. 38 illustrates a conventional graph of the curve of flying heightversus TFC actuation as it varies at different altitudes.

DESCRIPTION

Embodiments described below in context of the devices are analogouslyvalid for the respective methods, and vice versa. Furthermore, it willbe understood that the embodiments described below may be combined, forexample, a part of one embodiment may be combined with a part of anotherembodiment.

In this context, the storage device as described in this description mayinclude a memory which is for example used in the processing carried outin the storage device. A memory used in the embodiments may be avolatile memory, for example a DRAM (Dynamic Random Access Memory) or anon-volatile memory, for example a PROM (Programmable Read Only Memory),an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or aflash memory, e.g., a floating gate memory, a charge trapping memory, anMRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase ChangeRandom Access Memory).

In an embodiment, a “circuit” may be understood as any kind of a logicimplementing entity, which may be special purpose circuitry or aprocessor executing software stored in a memory, firmware, or anycombination thereof. Thus, in an embodiment, a “circuit” may be ahard-wired logic circuit or a programmable logic circuit such as aprogrammable processor, e.g. a microprocessor (e.g. a ComplexInstruction Set Computer (CISC) processor or a Reduced Instruction SetComputer (RISC) processor). A “circuit” may also be a processorexecuting software, e.g. any kind of computer program, e.g. a computerprogram using a virtual machine code such as e.g. Java. Any other kindof implementation of the respective functions which will be described inmore detail below may also be understood as a “circuit” in accordancewith an alternative embodiment.

The amount of data to be stored on data storage devices is increasing.Thus, it may be desired to provide data storage devices with a high datastorage capacity.

Reducing the bit aspect ratio (BAR) may be a way to further increase theareal density of HDD (hard disk drives) in the future. Shingled writingwith a sharp field gradient may be a promising approach to furtherreduce the track pitch for higher KTPI (or kTPI, or kilo TPI, whereinTPI may stand for tracks per inch). The reader width may be adetermination factor for achievable areal density. With noise limitationand also fabrication tolerance limit, the further reduction of the trackwidth of a reader may be an issue with a big challenge, especially,reducing BAR towards 1. According to various embodiments, devices andmethods may be provided to enable reading data from a track pitch whichis narrower than its reader size.

According to various embodiments, devices and methods may be providedfor shingle reading with a wide reader.

FIG. 1A shows a flow diagram 100 illustrating a method for reading datafrom a storage medium using a reader in accordance with an embodiment.The reader may include for example with one reader head or a pluralityof reader heads, for example multiple readers on a single slider. In102, a first signal may be read with a reader head of the reader at afirst position of the storage medium. In 104, a second signal may beread with a reader head (for example the same reader head used forreading a the first position of the storage medium, or another readerhead of the reader) at a second position of the storage medium. In 106,data stored at a pre-determined position of the storage medium may bedetermined based on the first signal and based on the second signal. Thesame procedure can be achieved by using multiple readers head to pick upmultiple location signals at one read process. The multiple read headsmay have a fixed reader offset in both down track and cross track. Thismay provide a simple way for reconstructing the narrower trackinformation from wide reader.

In other words, in a method according to various embodiments, aplurality of readings may be made, wherein a reader head may be atdifferent positions for each of the plurality of readings (for exampleat a first position for the first reading, at a second position for thesecond reading, and so on). Then, based on the plurality of readings,data that is stored on one pre-determined position of the storage mediummay be determined based on the plurality of readings. The plurality ofreadings can be based on multiple read heads. According to variousembodiments, in a single reader head (in other words: in a reader withonly one reader head) signals may be read sequentially in a pluralityreads. In a multiple readers head (in other words: in a head with aplurality of reader heads) signals may be read parallel in a plurality(parallel or simultaneous) reads. Multiple readers head mean many thatthere is provided a plurality of reader sensors in one head. Each readermay pick up a signal at different location simultaneously.

According to various embodiments, it may be understood that the readerhead at a position may be understood as the center of the reader head on(or above) the position of the storage medium.

The storage medium may for example be a magnetic storage medium, forexample a hard disc drive.

According to various embodiments, the storage medium may include aplurality of tracks. Each track may have a width (or a pitch) smallerthan a width of a reader head of the reader.

According to various embodiments, for at least one of the first positionor the second position a reader head of the reader may cover a firsttrack and a second track.

According to various embodiments, the pre-determined position mayinclude or may be one of a pre-determined position on the first track ora pre-determined position on the second track.

According to various embodiments, the first track and the second trackmay be adjacent.

According to various embodiments, the method may further include:reading a plurality of signals. For each signal, a reader head of thereader may be at a different position of the storage medium. The methodmay further include determining data stored at the pre-determinedposition of the storage medium based on the plurality of signals. Forexample a multiple readers head may be used to pick up multiple signalsat different location.

According to various embodiments, the method may further include:determining the data stored at the pre-determined position of thestorage medium based on a de-convolution.

According to various embodiments, the method may further include:reading a frequency burst signal with a reader head of the reader at aposition of the storage medium, wherein the position includes afrequency burst provided before a data track on the storage medium.According to various embodiments, the method may further includedetermining the data stored at the pre-determined position of thestorage medium may further be based on the frequency burst signal.

According to various embodiments, the storage medium may include aplurality of tracks having a width (or a pitch) smaller than a width ofa reader head of the reader; and the storage medium may include at leastone track having a width (or a pitch) equal to or larger than the widthof the reader head.

According to various embodiments, the first position may be differentfrom the second position.

According to various embodiments, determining of the data stored at apre-determined position of the storage medium may further be based ondetermining an amplitude coefficient, the amplitude coefficientindicating a contribution of data stored at the first position of therecording medium.

According to various embodiments, determining of the data stored at apre-determined position of the storage medium may further be based ondetermining an amplitude coefficient, the amplitude coefficientindicating a contribution of data stored at the second position of therecording medium.

According to various embodiments, determining of the data stored at apre-determined position of the storage medium may further be based ondetermining a phase offset of data stored at the first position of therecording medium.

According to various embodiments, determining of the data stored at apre-determined position of the storage medium may further be based ondetermining a phase offset of data stored at the second position of therecording medium.

FIG. 1B shows a storage device 108 in accordance with an embodiment. Thestorage device 108 may include a storage medium 110. The storage device108 may further include a reader 112 (for example including one readerhead or a plurality of reader heads) configured to read a first signalwith a reader head of the reader at a first position of the storagemedium and configured to read a second signal with a reader head (forexample the same reader head used for reading a the first position ofthe storage medium, or another reader head of the reader) at a secondposition of the storage medium. The storage device 108 may furtherinclude a data determination circuit 114 configured to determine datastored at a pre-determined position of the storage medium based on thefirst signal and based on the second signal. The storage medium 110, thereader 112, and the data determination circuit 114 may be coupled witheach other, like indicated by lines 116, for example electricallycoupled, for example using a line or a cable, and/or mechanicallycoupled.

According to various embodiments, it may be understood that the readerhead at a position may be understood as the center of the reader head on(or above) the position of the storage medium.

The storage medium may for example be a magnetic storage medium, forexample a hard disc drive.

According to various embodiments, the storage medium 110 may include aplurality of tracks, each track having a width (or a pitch) smaller thana width of a reader head of the reader.

According to various embodiments, for at least one of the first positionor the second position a reader head of the reader may cover a firsttrack and a second track.

According to various embodiments, the pre-determined position mayinclude or may be one of a pre-determined position on the first track ora pre-determined position on the second track.

According to various embodiments, the first track and the second trackmay be adjacent.

According to various embodiments, the reader 112 may further beconfigured to read a plurality of signals. For each signal, a readerhead of the reader 112 (for example the same reader head (for examplethe single reader head of the reader) or different reader heads of thereader) may be at a different position of the storage medium 110. Thedetermination circuit 114 may further be configured to determine datastored at the pre-determined position of the storage medium 110 based onthe plurality of signals.

According to various embodiments, the determination circuit 114 mayfurther be configured to determine the data stored at the pre-determinedposition of the storage medium 110 based on a de-convolution.

According to various embodiments, the reader 112 may further beconfigured to read a frequency burst signal with a reader head of thereader 112 (for example the same reader head (for example the singlereader head of the reader) or different reader heads of the reader) at aposition of the storage medium including a frequency burst providedbefore a data track on the storage medium 110. The determination circuitmay further be configured to determine the data stored at thepre-determined position of the storage medium further based on thefrequency burst signal.

According to various embodiments, the storage medium 110 may include aplurality of tracks having a width (or a pitch) smaller than a width ofa reader head of the reader 112. The storage medium 110 may or may notinclude at least one track having a width (or a pitch) equal to orlarger than the width of the reader head 112.

According to various embodiments, the first position may be differentfrom the second position.

According to various embodiments, the determination circuit 114 mayfurther be configured to determine the data stored at a pre-determinedposition of the storage medium further based on determining an amplitudecoefficient, the amplitude coefficient indicating a contribution of datastored at the first position of the recording medium.

According to various embodiments, the determination circuit 114 mayfurther be configured to determine the data stored at a pre-determinedposition of the storage medium further based on determining an amplitudecoefficient, the amplitude coefficient indicating a contribution of datastored at the second position of the recording medium.

According to various embodiments, the determination circuit 114 mayfurther be configured to determine the data stored at a pre-determinedposition of the storage medium further based on determining a phaseoffset of data stored at the first position of the recording medium.

According to various embodiments, the determination circuit 114 mayfurther be configured to determine the data stored at a pre-determinedposition of the storage medium further based on determining a phaseoffset of data stored at the second position of the recording medium.

A shingled magnetic recording (SMR) zone may include a plurality ofshingled or overlapping tracks. For instance, a first track may beoverlapped by a second track immediately adjacent (i.e. contiguous) tothe first track and the second track may be overlapped by a third trackimmediately adjacent (i.e. contiguous) to the second track. The width ofa writing element may be larger than the track pitch (i.e. thenon-overlapped portions of the width of a data track).

According to various embodiments, a de-convolution method may beprovided to enable a larger reader to read data from track pitch whichis narrower than its reader size. Simulation results and experimentaldata will be described below to demonstrate the feasibility of thevarious embodiments. Furthermore, according to various embodiments, asubsequent suitable shingle writing scheme and an implementation ofcorrelation ratio by using a dedicated frequency burst before a datatrack may be provided, like will be described in more detail below.

FIG. 2 shows a schematic illustration 200 of a reader for shingledtracks on a recording medium. In the shingled magnetic recording, ashingled track (for example a first shingled track 204, a secondshingled track 206, and a third shingled track 208) may be designed tobe narrower than the reader width (for example as indicated by anexemplary size of reader head 210) as shown in FIG. 2. It will beunderstood that although three shingled tracks 204, 206, and 208 areshown in FIG. 2, any number of shingled tracks may be provided. At thelast track of shingled zone, the track 202 may be wider than the reader(or reader head) such that the reader may reproduce the integrity singletrack signal. This signal may be called the reference track signal. Whenthe reader moves to the shingled tracks, the reader covers 2 tracks inone reading. Subsequently, the reader picks up a number of tracks ofdata or a page of data. According to various embodiments, ade-convolution process may be applied to get the data back (in otherwords: to determine the data stored in the recording medium).

For example, at a first position 212, the reader may read a first signalfrom the wide track 202 only. The first signal may correspond to thedata stored in the wide track 202. At a second position 214, the readermay read a second signal which may be a combination or a mixture ofsignals from (or stored in) the wide track 202 and from (or stored in)the first shingled track 204. By knowing the signal from the wide track202, the data stored in the first shingled track 204 may bereconstructed. At a third position 216, the reader may read a thirdsignal which may be a combination or a mixture of signals from (orstored in) the first shingled track 204 and from (or stored in) thesecond shingled track 206. By knowing the signal from the first shingledtrack 202, the data stored in the second shingled track 206 may bereconstructed. At a fourth position 218, the reader may read a fourthsignal which may be a combination or a mixture of signals from (orstored in) the second shingled track 206 and from (or stored in) thethird shingled track 208. By knowing the signal from the second shingledtrack 204, the data stored in the third shingled track 208 may bereconstructed.

A de-convolution method can be either using a fixed-offset adjacenttrack subtraction method or amplitude coefficient estimation method toreconstruct the shingle track information.

FIG. 3 illustrates an example of a read back process of a de-convolutionmethod. For example, a fixed-offset adjacent track subtraction methodmay be shown. If the magnetic reader width (MRW 304, or short “readerwidth” or “read width”), which for example may be measured in nm, isdefined to be larger than the Magnetic shingle Track width (MTW 302, orshort “track width”), which for example may be measured in nm, theequation of the read back signal X_(n) at location n may be

$\begin{matrix}{X_{n} = {{{A_{n}T_{1}} + {B_{n}T_{2}}} = {{\frac{{MRW} - {nM}}{MRW}T_{1}} + {\frac{nM}{MRW}T_{2}}}}} & (1)\end{matrix}$where A may be the ratio of the amplitude signal contributed by a firstdata track, for example the data track T₁, and B may be the ratio of theamplitude signal contributed by a second data track, for example thedata track T₂, wherein M 306 may be a step size (which may for examplebe measured in nm), n may be a step index, nM may be an offset (forexample measured in nm) from the adjacent read, nM may be smaller thanor equal MTW 302 (in other words: nM≦MTW), and A+B=1 (for example tonormalize against MRW 304). For this example scheme, the MRW 304 may belarger than MTW 302 (of the second track T2). But MRW 304 may be smallerthan the MTW of T1 (of the first track). The first MTW may be largerthan MRW to provide a good signal without adjacent track interferencefor the subsequent track data recovery. Furthermore, it will beunderstood that X_(n) corresponds to an n step offset from an initialposition.

In the following, a fixed-offset adjacent track subtraction methodaccording to various embodiments will be described.

According to various embodiments, a method may be provided which takesthe subtraction of two adjacent tracks read back signal with a knownread offset. Generic equations derived from equation (1) may be shown asbelow:

$\begin{matrix}{{X_{n} - X_{n - 1}} = {{{- \frac{M}{MRW}}T_{1}} + {\frac{M}{MRW}T_{2}}}} & (2) \\{{X_{n} - X_{0}} = {{{- \frac{nM}{MRW}}T_{1}} + {\frac{nM}{MRW}T_{2}}}} & (3)\end{matrix}$

It will be understood that the equations (2) and (3) may be derived fromequation (1). The only different of them may be the step size or readoffset.

Equation (2) illustrates the results of direct subtraction of 2 adjacenttrack with a known read offset between the signal. Equation (3) shows aspecial case where X₀ in equation may be referring to the signal onlysolely is contributed by the wide track T₁. Equations (2) and (3) mayhave a unique characteristic whereby the coefficient of T₁ and T₂ may beequal. The coefficient is defined as ratio of read offset to MRW.Substituting the known T₁ from reference track, X₀, T₂ may bereconstructed.

A simulation may be carried out to demonstrate the devices and methodsaccording to various embodiments.

FIG. 4 shows an illustration 400 of a simulated shingle writing schemewhich includes 5 data track, T₁ to T₅ (for example T₁ (402), T₂ (404),T₃ (406), T₄ (408), and T₅ (410)).

T₁ may be the last shingle writing zone (which may also be referred toas the reference track) where the MTW may be set to be 12 units(arbitrary unit length) whereas the track width of the other tracks maybe set to be 6 units. In this simulation, the MRW may be assumed to besame size as reference track width, 12 units.

FIG. 5 shows an illustration 500 of a mapping of the reader's read backsignal X_(n) by moving 1 unit/step using equation 1. The resultant X_(n)is later subtracted by X_(n−1)(equation 2 and 3) as described in thefixed-offset adjacent track subtraction method. FIG. 6 shows theresultant processed signal of fixed-offset adjacent track subtractionmethod as in the illustration 600. Subsequently T₂ to T₅ signal may bereconstructed as shown in illustration 700 of FIG. 7. by solving theequation.

In the following, deconvolution by amplitude coefficient estimationmethod according to various embodiments will be described. For example,X_(n)=AT₁+BT₂; and the fixed offset adjacent track method according tovarious embodiments as described above does not need to know what iscomponent A and B. By subtracting X_(n) to X_(n−1), it may be solved forthe T₁ and T₂. In the amplitude coefficient estimation method accordingto various embodiments, a method to estimate A and B may be used inorder to solve or reconstruct the T1 and T2. According to variousembodiments, the fixed offset adjacent track method may use a multiplereader configuration.

FIG. 8 shows the illustration 800 of a read back signal X₁ and X₂ over 2shingle tracks T₁ and T₂:X ₁ =aT ₁ +bT ₂X ₂ =cT ₁ +dT ₂  (4)Equation (4) can be solved to reconstruct T₁ and T₂ if coefficient a, b,c and d are accurately estimated. Equation 5 shows the reconstructedshingle track T₁ and T₂.

$\begin{matrix}{{T_{1} = \frac{X_{1} - {bT}_{2}}{a}}{T_{2} = \frac{X_{2}}{{c\left( \frac{X_{1} - b}{a} \right)} + d}}} & (5)\end{matrix}$

FIG. 9 shows an illustration 900 of general schematic of de-convolutionmethod using the amplitude coefficient estimation method according tovarious embodiments. For illustration purpose, the scheme shows only 2read back signals 902 (for example X₁ and X₂) to describe the workingprinciple. According to various embodiments, the numbers of read backsignals may not be limited. The 2 input signal may be sequentially readby a single reader head (sequential plurality read) or parallel read bymultiple reader head (parallel plurality read). In real HDD application,signal X₁ and X₂ may be subjected to down track jitter noise and crosstrack positioning jitter (amplitude coefficient). A de-convolutionprocess may require that both signals are phase synchronized in downtrack direction and track positioning jitter needs to be captured in thetrack amplitude coefficient a, b, c and d. The individual read backsignal may go through a phase detector and amplitude coefficientdetector 904 to estimate phase offset and a, b, c, d value. The phaseoffset of X₂ may be adjusted by a phase adjuster 906 according to X₁ toproduce synchronized signal. T₁ and T₂ may be reconstructed (for exampleby de-convolution 908 following the de-convolution process as describedin equation (5).

In sequential plurality reading, a de-convolution scheme may utilize thebenefits of inherent wide track of shingle write as shown inillustration 1000 of FIG. 10. If the input signal 1002 is from widetrack (as determined in 1004), the read back signal X may directly bestore in a memory 1006 as data track T₁. Subsequently, a read backsignal X_(n) from shingle track may go through a phase detector andamplitude coefficient detector 1008 to determine phase offset of X_(n)with respect to T_(n) from memory and estimate the amplitudecoefficient, a and b. Output of the detector will go through a phase andamplitude adjuster 1010 to produce synchronized signal beforedeconvoluting (in 1012) to reconstruct track info of T_(n+1). The schemewill continue to use T_(n+1) to reconstruct the next track signal.

There may be many ways to determine the phase offset and amplitudecoefficient. Various embodiments will be described. Most of thefollowing description is based on the scheme illustrated in FIG. 10. butthe principle illustrated may also be applied in scheme illustrated inFIG. 9.

FIG. 11 shows a phase and amplitude detector scheme 1100 usingcross-correlation method or matching filter method to recover thesignal. The reference signal X₁ in memory 1102 may first cross-correlate(or match) itself using a match filter 1104 to produce a referenceamplitude, A₀. Subsequence shingle read signal X₂ may match with thereference signal X₁ (for example using a further match filter 1106) toproduce the phase difference P₁ and amplitude A₁. The amplitudecoefficient, α may be a normalization of amplitude A₁ with respect toA₀. After the phase and amplitude adjuster, the shingle track data maybe reconstructed.

The matching filter scheme may have additional benefits. If we dividethe reference data and shingle data into smaller section as shown inillustration 1200 of FIG. 12, a higher sampling of amplitude coefficienta_(i)([A₁/A₀]_(i)) may be obtained. The amplitude coefficient maytranslate into the position error signal (PES). Thus, a continuous PESsystem may be extracted from the arbitrary data pattern in the shinglereading system. A dual stage PES servo control system 1300 in FIG. 13may then be provided. During the wide track read back, the continuousservo from arbitrary data pattern may not available. The conventionaldrive servo may be applied as the wide track requires less TPI (tracksper inch) resolution. When the head is reading the narrow track, it mayneed high TPI capability and the matched filter may generate precise PEScontinuously or higher bandwidth servo control. Besides, higher samplingrate of amplitude coefficient α_(i)=(A₁/A₀)_(i), the devices and methodaccording to various embodiments may have ability to compensate the PESerror during the recovery of shingle track signal and hence may make thesystem more tolerate to PES error and relax the need of high bandwidthservo control system. Combination of high PES bandwidth and highsampling rate of amplitude coefficient may make the system more robustin shingle read system.

FIG. 14 shows another phase and amplitude detector scheme 1400. It usesconventional drive servo preamble to achieve phase synchronization anduses additional multi-frequency data pattern to determine the amplitudecontribution factor of reference track in shingle read track. FIG. 15shows an illustration 1500 wherein the additional single frequency datapattern is written at the beginning of data sector or at the end of datasector. The adjacent shingle track may write a different frequency fordifferentiation. Hence a multi-frequency data pattern is formed acrossthe shingle track. In the shingle read track, the amplitude coefficient,a, b, c, d may be estimated through the different frequency burst. In 2frequency system, the first method to estimate a value may be throughiteration. Base on FIG. 15, the signal X₁ is the wide track frequencyburst, while signal X₂ is the shingle read track dual frequency signal.By iterating “a” value during subtraction of X₂ to X₁, until the maximumSNR of shingle track T₂ (frequency burst region) is achieved. Thiscondition achieved when the T1 signal is at minimum in frequency signal.At the beginning of each data track, a frequency burst may be written.For example, a first track T₁ may have a first frequency F₁ and a secondtrack T₂ may have a second frequency F₂. When the head read is at theposition in between the 2 tracks (this may be a second read, while wehave the first read at T₁ wide track), it may follow the equation shownin FIG. 5 (T₂=X₂−aX₁). At each iteration of subtracting X₂ from X₁(X₁=T₁), the “a” value may be adjusted until the resultant T₂ signal hasleast component of T₁ signal. This may be reflected in SNR as we the FFT(fast Fourier transform) of F₂ may be compared against F₁ signal.Another method to estimate amplitude coefficient may be through theamplitude detection of frequency burst. The value may become:

$\begin{matrix}{a = \frac{A_{F\; 1} - A_{F\; 2}}{A_{F\; 1} + A_{F\; 2}}} & (6)\end{matrix}$

FIGS. 16 and 17 showing the de-convolution results from the “a”iteration method. FIG. 16 show the signal image comparison 1600 betweenwide track data X₁, shingle read track X₂, original shingle track dataT_(2-o), and recover shingle data T₂. The reconstructed shingle track T₂look alike as original shingle track T_(2-o). In FIG. 17, a chart 1700shows that without signal recovery, the shingle read track SNR is 4.76dB compared to the original shingle track NT31 at 11.97 dB. The widetrack signal WT31 may have relatively larger SNR compared to the NT31 asthe wide reader will pick up the media noise outside of the narrowtrack. The reconstructed signals (1 or 2) may have SNR relatively closeto the NT31. It shows that the de-convolution scheme according tovarious embodiments may reproduce a signal of a shingle track.

For the third phase and amplitude coefficient detector scheme, a buriedlayer dedicated servo system, like will be described in more detailbelow, may be used to realize the wide reader shingle magnetic recordingsystem. FIG. 18 shows the example 1800 of dedicated multi-frequencyservo which may generate both continuous PES and phase synchronizationsignal. If two frequencies burst F1 and F2 are written in the dedicatedservo layer below the data layer, and the reader is position to cover 2servo track, the read back signal can generate the PES signal bydetecting the amplitude of the frequency burst as shown in equation (7).

$\begin{matrix}{{PES} = \frac{A_{F\; 1} - A_{F\; 2}}{A_{F\; 1} + A_{F\; 2}}} & (7)\end{matrix}$It may be a similar concept to equation (6) in determining the amplitudecoefficient of reference track. The mixing frequency F1 and F2 togetherwith the low pass filter may generate an output sine wave with frequencyF1−F2. This signal may be used as phase synchronization signal. Besides,phase offset can be detected through the preamble signal as describedabove.

The deconvolution scheme shows in FIG. 9 is to have a wide track as thereference track in a data zone. However, in reading process, it may needto have start reading from the wide track to retrieve the data. It mayincrease the reading time if only a few data track is needed out of thewhole data zone. Hence, a suitable shingle writing scheme 1900 shown inFIG. 19 can be applied to reduce the reading time by increasing thenumber of wide tracks 1902 in the data zone. For example, at each nshingle narrow write track 1904, a wide track (MTW≧MRW) may be writtenas the reference signal. This wide track 1902 may serve as the referencetrack to recover the both sides of narrow shingle read track. This mayavoid the need to read the whole data zone if only a small portion ofdata is need. Besides, this writing scheme may have advantages bylimiting the number of narrow shingle track to be recovered withreference to the wide track. For example, the scheme showed in FIG. 19indicates that at every 2 narrow shingle tracks will have a wide track.Since each wide track may be the reference for both adjacent narrowshingle tracks, the scheme may provide a certain quality of SNR to bemaintained in the shingle reading scheme. It may benefit especially tothe case where the subsequent narrow recovered track may inherence somesignal deterioration. If the signal becomes the next reference track forthe next shingle reading track recovery, the error may accumulate andSNR may worsen.

In the following, a buried layer dedicated servo system (for examplerelating to methods and apparatus for hard-disk drive system operationmonitoring and self-adjustment) according to various embodiments will bedescribed.

The following generally relates to data storage devices, and moreparticularly relates to hard disk drive (HDD) data storage products,including methods and apparatus for monitoring and adjusting theoperation thereof.

Hard disk drives include a recordable medium and a head which is mountedto move above the recordable medium as the medium spins. As hard diskdrives are designed to smaller and smaller sizes and the medium isdesigned to store more and more information on narrower and narrowertracks, it is imperative that the relative positions of the rotatingmedium and the moving head be monitored and other parameters such asrelative motion and speed variations be monitored. Such monitoring isneeded in order to correct any errors before they become too great.However, today's monitoring techniques are insufficient for the trackwidths, height tolerances and other parameters.

Thus, what is needed are robust monitoring and self-adjustmenttechniques for hard disk drives that are compatible with futureultra-thin, greater storage hard disk drives. Furthermore, otherdesirable features and characteristics will become apparent from thesubsequent detailed description, taken in conjunction with theaccompanying drawings and this background of the disclosure.

According to the Detailed Description, a method for monitoring hard diskdrive operation in a hard disk drive system is provided. The hard diskdrive system includes a spindle, a disk and a head. The method includesthe steps of writing a wide pattern having a predetermined frequency ona track of a hard disk drive medium, generating a readback signal byreading the wide pattern from the track, processing the readback signalby mixing the readback signal with a reference signal to obtain a summedsignal and a difference signal, and filtering the summed signal by afilter centered around the difference signal to generate a measurementsignal corresponding to a relative speed change of the spindle and ahead-to-disk motion.

In accordance with another aspect of the present embodiment, a methodfor monitoring operation of a hard disk drive system is presented. Thehard disk drive system includes a disk medium including a buried servolayer having a first frequency of data on a first track and a secondfrequency of data on a second track, the second track adjacent to thefirst track. The method includes the steps of reading a readback signalby a head positioned at the middle of the first track and the secondtrack, filtering the signal by a first filter centered at the firstfrequency to extract a first component signal, filtering the signal by asecond filter centered at the second frequency to extract a secondcomponent signal, combining the first component signal and the secondcomponent signal to generate a synchronization signal comprisingdowntrack information. The downtrack information may include spindlespeed variation, spindle speed jitter, and relative head-disk vibrationin the downtrack direction.

In accordance with yet another aspect of the present invention, a methodfor measuring flying height of a head over a disk medium in a hard diskdrive (HDD) system is provided. The HDD system includes a disk mediumhaving a buried servo layer with a first frequency of data on a firsttrack and a second frequency of data on a second track, the second trackadjacent to the first track. The method includes the steps of reading areadback signal by a head positioned at the middle of the first trackand the second track, filtering the signal by a first filter centered atthe first frequency to extract a first component signal, filtering thesignal by a second filter centered at the second frequency to extract asecond component signal, combining the first component signal and thesecond component signal using Wallace equations to generate asynchronization signal comprising flying height information. A furtheraspect includes developing a table of operational parameters for variouspressures and temperatures from the flying height information forimproved HDD system operation.

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background of the invention or the followingdetailed description of the invention. In this detailed description,three embodiments will be discussed: a novel and improved technique forrelative head-disk motion and spindle speed variation measurement, anovel and improved technique for down-track synchronization in adedicated servo based magnetic recording system, and a novel andimproved technique for flying height monitoring in dedicated servo basedmagnetic recording system.

A new embodiment is presented to measure, in addition to spindle speedvariation, the relative head-disk downtrack motion. Unlike conventionalapproaches such as approaches using hall sensors and rotary encoders orapproaches using back electromagnetic field (EMF) measurement fordetermining spindle speed, the present embodiment uses written-ininformation on a disk to provide continuous and real-time informationabout relative head-disk motion, including the effects of relativehead-disk vibration. In addition, the present embodiment does notrequire additional components in a hard disk drive (HDD) implementationexcept firmware implementation of the present embodiment and a frequencysource to be provided by the HDD system on chip (SOC) circuitry.

Current measurement techniques for spindle speed are typicallyimplemented via rotary encoders (optical), hall sensors or measurementof back EMF. For a hard disk drive (HDD) which uses brushless DC (BLDC)motors and performs spindle speed measurement, such measurement can beaccomplished through Hall sensors built into the motor. In addition itis also possible, depending on the driving circuitry, to measure spindlespeed from back EMF.

However, all these methods provide only information on the rotationalspeed of the spindle and, therefore, are unable to provide the actualrelative head-disk speed or motion which is affected by other effectssuch as head-disk vibrations. In addition, the need to further increaserecording density means that current and future HDDs will move towardsvery few grains/bit recording. This puts added stress on the ability towrite accurately on the magnetic bits. The need for accurate andsynchronized writing means that spindle speed variation, jitter andundesired relative head-disk motion and vibration need to be kept verysmall. At the same time, the ability to accurately measure and quantifysuch spindle speed variation, jitter and undesired relative head-diskmotion and vibration at high resolution becomes very important.

The present embodiment presents a method and approach which can, inaddition to measuring the spindle speed and speed variations, alsoprovide measurement for downtrack relative motion and vibration betweenhead and disk at high resolution. Referring to FIG. 20, a diagram 2000depicts a first approach for real time spindle speed variation andrelative head-disk motion measurement. First, a pattern 2002 is writtenon a track on the disk preferably using a wide writer head. This widetrack pattern 2002 will reduce the off-track interference which candegrade a readback signal 2004.

The readback signal 2004 is read back from the wide track pattern 2002at a frequency f 106. Similar to a rotary encoder scheme, the higher thefrequency f 2006 used, the better the resolution. Since the achievable“encoded” resolution is limited only by a bandwidth of the read-write(RW) head and a disk media combination, a very high frequency in thehundreds of megahertz can be used, enabling an approach which is farsuperior to any conventional rotary encoder scheme. However, in order tostrike a balance between signal to noise ratio and resolution, afrequency of around 80 MHz to 150 MHz for current HDDs is preferred.

Subsequently, the RW head is positioned over the written track 2002 andreads back the written track in a continuous fashion. By using areference clock signal 2008 at frequency f+Δf, and mixing at a mixer2010 the reference clock signal 2008 with the readback signal atfrequency f 2012, a mixed signal having signal components at a summedfrequency 2f+Δf and a difference frequency Δf are obtained.

By using a filter 2014 (e.g., a band pass filter (BPF) or narrow bandfilter) centered at around frequency Δf, a resulting measurement signal2016 corresponding to relative spindle speed change and head-disk motionis obtained. It is possible to also use a BPF 2014 that is slightlyoffset from Δf depending on the range of relative speed variation to bemeasured. The width of the filter 2014 passband may also be a necessaryparameter of this embodiment. A sharper (smaller passband) filter 2014will provide a larger signal change (i.e., more sensitive) for the samerelative speed change, but may suffer from a limited range of speedsthat can be measured. Thus, a good trade-off between the target range ofmeasurement versus sensitivity is desired to achieve optimal results.

The above approach depicted in the diagram 2000 provides very highresolution. However, one drawback of this approach is that themeasurement signal generated is not monotonously increasing ordecreasing. Since the signal peaks at a center frequency, themeasurement may sometimes be ambiguous. This may be especially true whenthe measurement range spans to the left and right of the peak, as shownin the signal amplitude vs. RPM graphs 2300, 2350 in FIGS. 23B and 23D.

A second approach is depicted in diagram 2100 of FIG. 21. This secondapproach alleviates any ambiguity problem that may be present in thefirst approach by using two matched filters 2104, 2106 instead of asingle filter 2014. The steps to generate the readback signal 2012 arethe same as the first approach where a wide track of a single frequencyis written and mixed at a mixer 2010 with a reference clock signal 2008of the same writing frequency. However, this second approach providesthe resulting mixed signal IF 202 to the two filters 2104, 2106, whereinthe first filter 2104 is centered at Δf+f₁ and the second filter 2106 iscentered at Δf−f₁, generating the filtered signals A and B,respectively. The frequency f₁ is a frequency passband offset within thebandwidth of the first and second bandpass filters 2104, 2106. Anormalization procedure such as (A−B)/(A+B) can then be applied by thecombiner 2108 to provide a monotonously increasing signal 2110 over therange of relative spindle speeds to be measured.

Referring to FIG. 22, a graph 2200 further illustrates this secondapproach. When measured signal ΔF is less than Δf 2202, the measuredsignal ΔF moves further into the passband of the B signal 2204 and awayfrom the passband of the A signal 2206. If ΔF is, instead, greater thanΔf 2202, the measured signal ΔF moves into the passband of the A signal2206 and away from the passband of the B signal 2204. Since the signal A2206 must increase when the signal B 2204 decreases and vice versa, theresulting signal (A−B)/(A+B) is monotonously increasing for themeasurement range between Δf+f₁ and Δf−f₁, thereby removing theambiguity. Depending on the measurement range required, appropriate f₁values and filter widths can be chosen for optimal results.

FIG. 23B shows experimental results in the graph 2300 obtained using thefirst approach for measurements on the air bearing spindle with ameasured spindle speed variation of 0.005%. FIG. 23D shows experimentalresults in the graph 2350 obtained using the first approach formeasurements on a HDD product. And FIG. 24B shows experimental resultsin the graph 2400 when the second approach is used on a HDD product.

The technology and approaches in accordance with the present embodimentcan be easily applied to present HDD products. Because no additionalcomponents are required except a reference clock and digital filtering,both of which may be easily provided by the HDD system on chip (SOC),large additional costs of implementation are avoided. Also, byimplementing the technology into a HDD system and its associatedfirmware, it is possible to use the technology not only during HDDmanufacturing/assembly and in failure analysis situations, but alsoduring normal use by end users.

In the manufacturing and assembly stage, HDD products after assemblycould go through a long process of checks including formatting andtesting of the media. For very large drives, this could take a longtime. Due to manufacturing tolerances and production yields, not allassembled products can work at the same recording density. If the endtested product is found to be unsuitable for a certain recordingdensity, it needs to be downgraded to a lower density level. A testapproach in accordance with the present embodiment could be applied, forexample, after drive assembly and prior to the formatting and testingstep to ascertain the quality of the assembled drive. If at this stage,a drive is found to be of a “lower quality” from measured large speedvariations, jitter or relative head-disk vibrations, then the drive canbe put to a lower density level immediately. Thus, a simple measurementin accordance with the present embodiment is enabled which could helpreduce the manufacturing cost by detecting the quality of the endproduct earlier without requiring expensive and extensive testing,thereby exemplifying an intelligent manufacturing approach.

The testing approach in accordance with the present embodiment is alsouseful for the HDD under normal use by end users. For example, it ispossible to program the drive for regular self-testing using the testingapproach in accordance with the present embodiment. Such self-testingcan be performed by the HDD when the drive is idle, thereby serving as aself-reliability check during the HDD's operable life. Any variations intest results can indicate potential drive problems and future failurethat need to be fed back to the user for remedial actions before acatastrophic failure actually occurs.

Finally, in a Failure Analysis (FA) situation, the FA process mayinclude running a test in accordance with the present embodiment andexamining the test results. A degrade in performance (e.g., increasedhead-disk vibration or variations in relative spindle speed) couldindicate the possible source of a problem to the drive engineer evenbefore a complete tear-down is warranted. Thus, the present embodimentcan also serve as a quick initial check for the FA process

In one aspect of the present invention, a method for monitoring harddisk drive operation in a hard disk drive system including a spindle, adisk and head is provided. The method includes the steps of writing apattern having a predetermined frequency on a wide track of a hard diskdrive medium, generating a readback signal by reading the pattern fromthe track, processing the readback signal by mixing the readback signalwith a reference signal to obtain a summed signal and a differencesignal, and filtering the summed signal by a filter centered around thedifference signal to generate a measurement signal corresponding to arelative speed change of the spindle and a head-to-disk motion.

The monitoring techniques in accordance with the present embodimentadvantageously use written-in information on the disk instead of relyingon external sensors such as Hall sensors or rotary encoders, therebyenabling the actual head-disk relative speed and motion to be measuredinstead of only the spindle speed variation (conventional approachesonly measure spindle speed but cannot know relative head-diskvibration). Also, the present embodiment can be implemented in firmwareon the HDD and does not require additional components like Hall sensors.Only a frequency source is required, and such frequency source can beprovided by the HDD system on chip (SOC). Additionally, the written-in(“encoded”) track on the disk media can be at a very high frequency,providing robust, high resolution of measurements, the resolution onlybeing limited by the Read/Write (R/W) capability of the head and mediacombination. Further, the present embodiment can be used in conjunctionwith existing spindle speed control schemes in HDD, and can be appliedto current HDDs as a means for qualification of HDD components (e.g.,the spindle).

As HDD technology moves towards fewer grains/bit recording as well asfuture configurations such as Two Dimensional Magnetic Recording (TDMR)and bit-patterned media, the need to be able to determine the locationof the write and read head versus the location of individual bitsbecomes very important. Thus, the availability of a synchronizationsignal to determine these locations is paramount. When utilizing a dualfrequency dedicated servo media, where the presence of a dedicated servomagnetic layer allows “always on” servo information, the possibilityarises to obtain a “continuously on” write synchronization signal. This“continuously on” signal does not only help with accurate writes onlocation sensitive media but also provides a means to detect and measuredown track and spindle vibration, speed and other conditions.

In accordance with a second aspect of the present embodiment, a newconfiguration is proposed to make use of the frequency based dedicatedservo signal to produce an always available write synchronization signalthat can allow bit location determination, as well as detection ofdowntrack vibration, spindle speed variation, and jitter. A dedicatedservo layer 2502 located below the data magnetic layer 2504 is shown inthe cutaway view 2500 in FIG. 25. Multi-frequency or dual frequencybased servo schemes can be utilized in the dedicated servo layer 2502. Aslider head 2510 includes a reader head 2512 and a writer head 2514 forreading and writing to the magnetic layers 2502 and 2504. The sliderhead 2510 also includes a heater 2516 for thermal fly height control(TFC) as known to those skilled in the art. It is important to know thevibration, speed variation and jitter information in order to enablesynchronized writing.

Referring to FIG. 26, a top planar view 2600 shows that the reader head2512 is positioned at the middle of two tracks 2602, 2604 to read backthe superposition of the signals from the two servo tracks 2602, 2604 inthe dedicated servo layer 2502. The signals from the two servo tracks2602, 2604 are two separate frequencies as shown in a graph 2606 (i.e.,a frequency F1 2608 and a frequency F2 2610).

The process to generate the synchronization signal is given in FIG. 27,including FIGS. 27A and 27B. Referring to FIG. 27A, a block diagram 2700shows that by applying analog filters or digital filters 2702, 2704centered at F1 and F2 frequencies 2608, 2610, respectively, to the readback signal 2706 respective frequency components can be extracted,namely frequencies A and B corresponding to the signals from servotracks f1 2602 and f2 2604, respectively. The signals can be furtherprocessed to generate a signal 2708 that can be used for writesynchronization write synchronization in, for example, Two DimensionMagnetic Recording (TDMR), as well as for the detection of downtrackvibration, spindle speed variation and jitter.

The readback signal 2706 from the dedicated servo system consists ofboth a data signal and a servo signal. Referring to FIG. 27B, the F1+F2signal 2720 from the filters 2702, 2704 (FIG. 27A) is processed usingfilters 2722, 2724 (either analog bandpass or low pass filters ordigital filters) to obtain the F1 and F2 components. The separate F1 andF2 signals are then mixed at a mixer 2726 and filtered by a low pass orband pass filter 2728 to generate a Sine (F1−F2) signal 2730 whichconstitutes the synchronization signal. As the synchronization signal2730 is obtained entirely from the written-in dedicated servo signals(F1 and F2), no external reference clock or oscillator is required. Thismeans that the synchronization signal 2730 avoids any phase andfrequency drift that is common when an external reference clock is used.At the same time, the synchronization signal 2730 will fully reflectdowntrack changes in the HDD system such as spindle speed variation andjitter, and relative head-disk vibration in the down track direction.

FIGS. 28A and B depict three traces 2802, 2804, 2806 that show thesimulation results for the generation of the synchronization signal 2730from the dedicated servo signal. Referring to FIG. 29, simulationresults are depicted in a first trace 2900 that illustrates thesynchronization signal 2730 is resilient to relative changes in theamplitude of the servo F1 and F2 components which can occur if there isoff-track in the read-write head. Essentially by detecting the zerocrossing of the AC synchronization signal, effects of off-track whichcan manifest for example in a different amplitude of the synchronizationsignal are ignored. A second trace 2950 shows that the synchronizationsignal 2730 is responsive to a relative phase difference between F1 andF2 components. Referring to FIG. 30, the results 3000 further show theactual spinstand experimental results for generating the synchronizationsignal 2730, Sine (F1−F2).

The synchronization signal 2730 provides a means to know the location ofthe read head 2512 in the downtrack direction. For example, thesynchronization signal 2730 can be measured and can be translated into alocation in the downtrack direction. While a simplified approach countsthe number of zero-crossings from the start of a sector or index mark,other methods that can detect phase may also be used. The zero-crossingdetector approach is useful because it is not affected by changes in theamplitude of the synchronization signal 2730. By knowing the currentlocation of the read head 2512, it is possible to estimate the locationof the write head 2514. With a known location of the write head 2514,synchronized writing utilizing measurements in accordance with thepresent embodiment can accurately write on targeted magnetic bits.

In addition to synchronized writing, another advantageous use of thesynchronization signal 2730 is that it provides information on relativehead-disk motion and captures information including undesired jitter,vibration and shock. For example, a deviation or change to thesynchronization signal 2730 at a particular instant of time indicatesthat there is an event that has caused a disturbance in the downtrackdirection. Referring to FIG. 31, a graph 3100 shows an example whererelative head-disk speed suddenly increased for a short duration,resulting in a detected synchronization signal 2730 that has deviatedfrom the expected or normal signal. By monitoring the synchronizationsignal 2730 to detect deviations, ΔSine(F1−F2), it is possible to detectand measure events such as downtrack vibrations or changes in spindlespeed.

The ability to monitor downtrack changes and predict downtrack locationis advantageous. In the dedicated servo implementation in accordancewith the present embodiment, this is even more useful because suchmonitoring and measurement is available everywhere by virtue of the factthat servo track information is available everywhere on the disk. Byimplementing the invention into a HDD, for example through firmware inthe HDD system on chip (SOC), the monitoring and measurement can becomean important tool to detect HDD operational conditions such as excessiveshock or vibration and allow the HDD to respond quickly and takepreventive action to avoid failure and crash. Regular measurement of thevibration in accordance with the present embodiment can also help tomonitor reliability of the drive while in operation. Finally, thepresent embodiment provides a useful Failure Analysis tool to determinewhether the performance of the drive has degraded.

In accordance with this second aspect of the present embodiment, amethod for monitoring operation of a hard disk drive system having adisk medium including a buried servo layer having a first frequency ofdata on a first track and a second frequency of data on a second track,the second track adjacent to the first track, is provided. The methodincludes the steps of reading a readback signal by a head positioned atthe middle of the first track and the second track, filtering the signalby a first filter centered at the first frequency to extract a firstcomponent signal, filtering the signal by a second filter centered atthe second frequency to extract a second component signal, combining thefirst component signal and the second component signal to generate asynchronization signal comprising downtrack information. The downtrackinformation may include spindle speed variation, spindle speed jitter,and relative head-disk vibration in the downtrack direction.

In accordance with the present embodiment, written-in servo informationfor phase recovery is used. Thus, no additional information orprogramming is required. In addition, operation in accordance with thepresent embodiment does not require an external oscillator, therebyavoiding phase drift between a reference frequency and the written-inservo frequency. Also, operation in accordance with the presentembodiment is less affected by jitter and spindle speed variation sincethe (F1−F2) signal follows spindle jitter and speed variations due tousing the written-in servo information for timing. Further, thesynchronization signal 2730 is resilient to crosstrack and off-trackeffects (i.e., the AC zero crossing is unaffected by the relativestrength of servo components in the dual frequency servo layer). Thechanges to the synchronization signal 2730 reflect downtrack spindlejitter or speed variations, as well as relative head-disk vibration andshock. Thus, operation in accordance with the present embodiment canhelp HDD technology to achieve higher linear bits per inch recordingwhich is required to meet continued areal density growth.

In accordance with another aspect of the present embodiment, a newconfiguration is proposed to make use of a frequency based dedicatedservo signal to produce an always available Flying Height (FH) signalwith minimum off-track FH variation. This FH signal can be used as anadditional monitoring signal for contact detection and HDD reliability.

With the application of thermal Flying Height control (TFC) technology,the Wallace equation based in-situ FH testing technology becomes themajor way to measure the FH of Read/Write (R/W) heads. In theory, onesingle harmonic is good enough to detect the FH variation. But in actualapplication, the off-track of a read head changes the amplitude of areadback signal and may be misinterpreted as a change in Flying Height.This is one of the major sources of FH testing error. In order tominimize such FH testing error, a harmonic ratio method is typicallypreferred. It requires a write-in data pattern that can produce at leasttwo harmonics with harmonic signals of sufficient strength for accuratemeasurement. However, due to the special write-in pattern required onthe media, the FH value is not always available in HDDs. Further,conventional FH measurement techniques currently incorporate an acousticemission (AE) sensor or contact sensor into the magnetic read/write headof a HDD system to detect the contact point. The additional sensor(s)disadvantageously incur additional component cost for the HDD.

In accordance with a third aspect of the present embodiment, thededicated servo layer 2502 in the HDD disk medium is utilized to providean always available FH signal and advantageously offers minimization ofthe effects of off-track FH variation. This FH signal can be used as anadditional monitoring signal for contact detection and HDD reliability.Referring back to FIG. 25, the dedicated servo layer 2502 is locatedbelow the data magnetic layer 2504 in the disk medium. The flying height(FH) 2530 refers to the height of the head 2510 as it flies over thedisk medium. Multiple frequencies or a single frequency of data arestored on the servo tracks of the servo layer 2502. The reader 2512 ispositioned at the middle of two tracks 2602, 2604 to read back thesuperposition of the signal as shown in FIG. 26. Referring to the blockdiagram 3200 of FIG. 32, by applying analog or digital filters 2702,2704, the signal for the respective frequency components can beextracted from the readback signal 2706, and the amplitude of thesignals, namely A and B can be determined. The amplitude of the signalscan be further processed to produce a position error signal (PES) 3202,the synchronization signal 2708 and a flying height signal 3204.

Based on the Wallace Spacing Loss equation, the spacing Loss isexpressed as:A=e ^(−2πd/λ)  (8)where λ is the wavelength of the written data pattern and d is therelative change in spacing. Based on the amplitude ratio of the Wallaceequation, we can use five different Wallace spacing methods (obtainedfrom equation (8)) to calculate FH from the simultaneous two frequencyservo signal. They are:

$\begin{matrix}{{\Delta\; d} = {- \frac{\Delta\;{\ln(A)}*\lambda_{A}}{2\;\pi}}} & (9) \\{{\Delta\; d} = {- \frac{\Delta\;{\ln(B)}*\lambda_{B}}{2\;\pi}}} & (10) \\{{\Delta\; d} = {- {\frac{\Delta\;{\ln({AB})}}{2\;\pi}\left\lbrack \frac{\lambda_{A}\lambda_{B}}{\lambda_{B} + \lambda_{A}} \right\rbrack}}} & (11) \\{{\Delta\; d} = {- {\frac{\Delta\;{\ln\left( {A/B} \right)}}{2\;\pi}\left\lbrack \frac{\lambda_{A}\lambda_{B}}{\lambda_{B} - \lambda_{A}} \right\rbrack}}} & (12) \\{{\ln\left( {A + B} \right)} = {\ln\left\lbrack {{\mathbb{e}}^{- \frac{2\;\pi\; d}{\lambda_{A}}} + {\mathbb{e}}^{- \frac{2\;\pi\; d}{\lambda_{B}}}} \right\rbrack}} & (13)\end{matrix}$The above equations are based on ln(A), ln(B), ln(A*B), ln(A/B) andln(A+B). The respective equations are shown in FIG. 33. It isstraightforward to calculate FH based on the first four equations.However, for the case ln(A+B), a more complex equation is needed tocalculate FH and d needs to be calculated from a trial and error oriterative approach.

Alternatively, a simple calibration approach can be taken to determinethe FH instead of solving the complex equation (13). In this case, weuse the ln(A*B) case to calibrate FH for ln(A+B). The calibrationequation is shown below:

$\begin{matrix}{{\Delta\; d} = {\frac{\Delta\;{\ln\left( {A + B} \right)}}{\Delta\;{\ln\left( {A + B} \right)}_{x}} \times \Delta\; d_{x}}} & (14)\end{matrix}$where x is the relative TFC applied and Δd_(x) is the correspondingrelative FH measured by Δ ln(A*B)_(x). By normalizing the Δ ln(A+B)against Δ ln(A+B)_(x), the FH can be deduced.

FIG. 34, including FIGS. 34A and 34B, shows the touch down curve forrespective methods of FH measurement. A graph 3400 in FIG. 34A shows theFH measurement after one hundred times averaging, while a graph 3450 inFIG. 34B indicates an arbitrary instantaneous one point FH measurement.The information depicted in the graph 3450 shows that the FH measured bya single frequency is greatly affected by off-track error. This isfurther confirmed by the experimental results shown in a graph 3500 ofFIG. 35. For these results, the TFC was fixed. It can be seen that theoff-track FH variation error can be systematically studied by moving thereader sensor from −20 nm off-center to +20 nm off-center. However,ln(A+B) shows very little off-track FH variation error.

The instantaneous and always available FH signal can also be used as thecontact detection sensor. FIG. 36A shows the time domain FH signal. InFIG. 36A, a graph 3600 shows FH signals 3605 and 3615 at different TFCpowers. The FH signal 3615 shows a FH signal during normal operationwhile the vibration FH signal 3605 is clearly observed during the headdisk contact at a higher TFC power. FIG. 36B depicts a graph 2620 whichplots the root mean square (RMS) of the FH signal at different TFCpowers where signals 3622, 3624, 3626 are obtained using ln(A), ln(B)and ln(A+B), respectively. In the graph 2620, the RMS measurementsdepict a clear sudden increase of value at contact TFC. In some cases,the FH's RMS can even detect the FH vibration prior the AE sensor asshown in a graph 3700 of FIG. 37. This early detection can be attributedto pre-contact slider vibration. All of the above-mentioned FHmeasurement methods can be used as contact detection. Together with thecontinuous PES signal 3202, these give a two dimensional and fastresponse to near contact condition.

As the FH versus TFC actuation curve is different at different altitudes(as shown in a prior art example in graph 3800 of FIG. 38), it ispossible to create different FH calibration curves for differentaltitudes. One way is to calibrate and obtain curves under different airpressures corresponding to the different altitudes.

Subsequently, in actual HDD operation, by moving the operating pointthrough changing the TFC actuation (without going to contact) andmeasuring the change in FH for each TFC power used, it is possible todetermine the gradient, ΔFH/ΔPower_(TFC). This parameter can be used todetermine on which altitude curve the drive is operating. If thealtitude curve is correctly determined, then appropriate FH look-uptables could be used and unnecessary and undesired head disk contactcould be avoided by being able to apply the appropriate TFC power fordifferent altitudes.

The ability to determine the altitude curve on which the drive isworking is of great value. In present HDDs, it is difficult toincorporate an altitude sensor. Although drives have temperature sensors(e.g., thermistors), they generally do not have altitude sensors. Thismeans that current HDDs do not know whether they are being operated at ahigh altitude (e.g., greater than twenty thousand feet) or at sea level.When at a high altitude, the flying height of the head is lower andthere is increased chance of head-disk contact and reliability issues ifan improper TFC power (such as that suitable for sea level use) isapplied.

Appropriate look-up tables for HDD operation under different conditionsof pressure (altitude) and temperature can be generated by operation inaccordance with the present embodiment. Once these tables are generated,it is possible in accordance with the present embodiment to identify theright look up table to be used in actual drive operation, thus reducingthe reliability problems associated with HDD usage at differentaltitudes. Without calibrated look-up tables for different altitudes,the common approach for current HDDs is to spin down the disk or adjustthe TFC such that the head/slider comes into intermittent contact withthe disk. Once this is done, the flying height is then known from theamount of TFC actuation applied. However, this touch down approach maywear out the RW heads and also has the risk of head disk damage.Therefore, reduction or elimination of the need to touch down the RWhead is enabled by the present embodiment.

Another important advantage of the present embodiment is that the FHinformation is always available since the servo information is availableeverywhere for the dedicated servo HDD. Compared to current drives whereFH measurement can only depend on a few designated and specially writtenareas on the disk (if readback signal approach to determine FH is used),the always available FH information for the dedicated servo disk comesat little cost, but brings about great benefits.

In accordance with one aspect of the present invention, a method formeasuring flying height of a head over a disk medium in a hard diskdrive (HDD) system having a disk medium including a buried servo layerhaving a first frequency of data on a first track and a second frequencyof data on a second track, the second track adjacent to the first track,is provided. The method includes the steps of reading a readback signalby a head positioned at the middle of the first track and the secondtrack, filtering the signal by a first filter centered at the firstfrequency to extract a first component signal, filtering the signal by asecond filter centered at the second frequency to extract a secondcomponent signal, combining the first component signal and the secondcomponent signal using Wallace equations to generate a synchronizationsignal comprising flying height information. A second aspect includesdeveloping a table of operational parameters for various pressures andtemperatures from the flying height information for improved HDD systemoperation.

Thus it can be seen that methods for hard disk drive system operationhave been disclosed which provides many advantages over the drawbacks ofconventional HDDs. While several exemplary embodiments have beenpresented in the foregoing detailed description of the invention, itshould be appreciated that a vast number of variations exist, includingvariations as to the materials, structure and operation of the datastorage device.

It should further be appreciated that the exemplary embodiments are onlyexamples, and are not intended to limit the scope, applicability,dimensions, or configuration of the invention in any way. Rather, theforegoing detailed description will provide those skilled in the artwith a convenient road map for implementing an exemplary embodiment ofthe invention, it being understood that various changes may be made inthe function and arrangement of elements and method of play stepsdescribed in an exemplary embodiment without departing from the scope ofthe invention as set forth herein.

According to various embodiments, a method for monitoring hard diskdrive operation in a hard disk drive system including a disk having ahard disk medium on a surface thereof and being rotated by a spindlecoupled thereto, the hard disk drive system further including a head forwriting to and reading from the hard disk medium, may be provided. Themethod may include: writing a wide track pattern having a predeterminedfrequency on the hard disk drive medium; generating a readback signal byreading the wide track pattern; processing the readback signal by mixingthe readback signal with a reference signal to obtain a mixed signalincluding a summed signal and a difference signal; and filtering themixed signal by a filter having parameters determined in response to thedifference signal to generate a measurement signal corresponding to arelative speed change of the spindle and a head-to-disk motion.

According to various embodiments, the filtering step may include or maybe filtering the mixed signal by a filter centered around the differencesignal to generate the measurement signal.

According to various embodiments, the filtering step may include or maybe filtering the mixed signal by a filter slightly offset from thedifference signal to generate the measurement signal.

According to various embodiments, the generating the readback signalstep may include or may be generating the readback signal by reading thewide pattern from the track at a predetermined frequency f.

According to various embodiments, the predetermined frequency f may be apredetermined frequency greater than 50 MHz.

According to various embodiments, the predetermined frequency f may be apredetermined frequency in the range of 80 MHz to 150 MHz.

According to various embodiments, the processing the readback signalstep may include or may be processing the readback signal by mixing thereadback signal with the reference signal to obtain the mixed signalincluding the summed signal and the difference signal and wherein thereference signal comprises the predetermined frequency f plus thedifference signal.

According to various embodiments, the filtering step may include or maybe: filtering the mixed signal by a first bandpass filter havingparameters determined in response to the difference signal to obtain afirst filtered signal; filtering the mixed signal by a second bandpassfilter having parameters determined in response to the difference signalto obtain a second filtered signal; and combining the first filteredsignal and the second filtered signal to generate the measurement signalcorresponding to the relative speed change of the spindle and thehead-to-disk motion.

According to various embodiments, the first bandpass filter and thesecond bandpass filter may have equivalent bandwidths and wherein thefirst bandpass filter and the second bandpass filter have non-bandwidthparameters determined in response to the difference signal and afrequency passband offset f1 within the bandwidth of the first andsecond bandpass filters.

According to various embodiments, the first bandpass filter may havenon-bandwidth parameters determined in response to a sum of thedifference signal and the frequency passband offset f1 and wherein thesecond bandpass filter has non-bandwidth parameters determined inresponse to a difference between the difference signal and the frequencypassband offset f1.

According to various embodiments, a method for monitoring operation of ahard disk drive system having a disk medium including a buried servolayer having a first frequency of data on a first track and a secondfrequency of data on a second track, the second track adjacent to thefirst track, may be provided. The method may include: reading a readbacksignal by a head positioned at the middle of the first track and thesecond track; filtering the signal by a first filter centered at thefirst frequency to extract a first component signal; filtering thesignal by a second filter centered at the second frequency to extract asecond component signal; and combining the first component signal andthe second component signal to generate a synchronization signalcomprising downtrack information.

According to various embodiments, the method may further include thestep of utilizing the synchronization signal for write synchronizationin Two Dimension Magnetic Recording (TDMR).

According to various embodiments, the downtrack information may includeor may be one or more of spindle speed variation information, spindlespeed jitter information, and relative head-disk vibration in thedowntrack direction information.

According to various embodiments, the data on the first and secondtracks may include or may be written-in servo information for phaserecovery.

According to various embodiments, a method for measuring flying heightof a head over a disk medium in a hard disk drive (HDD) system, whereinthe disk medium includes a buried servo layer having a first frequencyof data on a first track and a second frequency of data on a secondtrack, the second track adjacent to the first track, may be provided.The method may include: reading a readback signal by a head positionedat the middle of the first track and the second track; filtering thesignal by a first filter centered at the first frequency to extract afirst component signal; filtering the signal by a second filter centeredat the second frequency to extract a second component signal; andcombining an amplitude of the first component signal and an amplitude ofthe second component signal using Wallace equations to generate asynchronization signal comprising flying height information.

According to various embodiments, the method may further include:developing a table of operational parameters for various pressures andtemperatures from the flying height information; and utilizing the tableof operational parameters for HDD system operation.

Methods and architecture for monitoring hard disk drive operation isprovided. The hard disk drive system provided includes a spindle, a headand a disk with a disk medium including a buried servo layer having afirst frequency of data on a first track and a second frequency of dataon a second track, the second track adjacent to the first track. Themethod includes the steps of writing a wide track pattern having apredetermined frequency on a track of a hard disk drive medium,generating a readback signal by reading the pattern from the track,processing the readback signal by mixing the readback signal with areference signal to obtain a mixed signal having a summed signal and adifference signal, and filtering the mixed signal by a filter centeredaround the difference signal to generate a measurement signalcorresponding to a relative speed change of the spindle and ahead-to-disk motion. In addition, filtering a readback signal generatedby the head when positioned at the middle of the first track and thesecond track with a first filter centered at the first frequency and asecond filter centered at the second frequency is used to generate asynchronization signal for determining spindle speed variation, spindlespeed jitter, and relative head-disk vibration in the downtrackdirection, for synchronizing writing in Two Dimensional MagneticRecording (TDMR) and for measuring continuous flying height informationbased on Wallace equations.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

What is claimed is:
 1. A method for reading data from a storage mediumusing a reader, the method comprising: reading a first signal with areader head of the reader at a first position of the storage medium,wherein the first signal includes a first portion corresponding to afirst track and a second portion corresponding to a second track;reading a second signal with the reader head of the reader at a secondposition of the storage medium, wherein the second signal includes athird portion corresponding to the first track and a fourth portioncorresponding to the second track; estimating, based on the firstportion and the second portion, (i) a first ratio of an amplitude of thefirst signal contributed by the first track with the reader head of thereader at the first position and (ii) a second ratio of the amplitude ofthe first signal contributed by the second track with the reader head ofthe reader at the first position; estimating, based on the third portionand the fourth portion, (i) a third ratio of the amplitude of the secondsignal contributed by the first track with the reader head of the readerat the second position and (ii) a fourth ratio of the amplitude of thesecond signal contributed by the second track with the reader head ofthe reader at the second position; and determining data stored at apre-determined position of the storage medium based on the estimatedfirst ratio, the estimated second ratio, the estimated third ratio, andthe estimated fourth ratio, wherein the storage medium comprises aplurality of tracks including the first track and the second track, eachtrack having a width smaller than a width of the reader head of thereader.
 2. The method of claim 1, wherein for at least one of the firstposition or the second position the reader head of the reader covers thefirst track and the second track.
 3. The method of claim 2, wherein thepre-determined position comprises one of a pre-determined position onthe first track or a pre-determined position on the second track.
 4. Themethod of claim 2, wherein: the first track is adjacent to the secondtrack.
 5. The method of claim 1, further comprising: reading a pluralityof signals, wherein for each signal the reader head of the reader is ata different position of the storage medium; and determining data storedat the pre-determined position of the storage medium based on theplurality of signals.
 6. The method of claim 1, further comprising:reading a frequency burst signal with the reader head of the reader at aposition of the storage medium comprising a frequency burst providedbefore a data track written at the same time when data is written on thestorage medium; wherein determining the data stored at thepre-determined position both down track and cross track of the storagemedium is further based on the frequency burst signal.
 7. The method ofclaim 1, wherein: the storage medium comprises a plurality of trackshaving a width smaller than a width of the reader head of the reader;and the storage medium comprises at least one track having a width equalto or larger than the width of the reader head of the reader.
 8. Themethod of claim 1, wherein: determining the data stored at thepre-determined position of the storage medium includes determining aphase offset of data stored at the second position of the recordingmedium.
 9. A storage device comprising: a storage medium; a readerconfigured to (i) read a first signal with a reader head of the readerat a first position of the storage medium, wherein the first signalincludes a first portion corresponding to a first track and a secondportion corresponding to a second track, and (ii) read a second signalwith the reader head of the reader at a second position of the storagemedium, wherein the second signal includes a third portion correspondingto the first track and a fourth portion corresponding to the secondtrack; and a data determination circuit configured to estimate, based onthe first portion and the second portion, (i) a first ratio of anamplitude of the first signal contributed by the first track with thereader head of the reader at the first position and (ii) a second ratioof the amplitude of the first signal contributed by the second trackwith the reader head of the reader at the first position, estimate,based on the third portion and the fourth portion, (i) a third ratio ofthe amplitude of the second signal contributed by the first track withthe reader head of the reader at the second position and (ii) a fourthratio of the amplitude of the second signal contributed by the secondtrack with the reader head of the reader at the second position, anddetermine data stored at a pre-determined position of the storage mediumbased on the estimated first ratio, the estimated second ratio, theestimated third ratio, and the estimated fourth ratio, wherein thestorage medium comprises a plurality of tracks including the first trackand the second track, each track having a width smaller than a width ofthe reader head of the reader.
 10. The storage device of claim 9,wherein: for at least one of the first position or the second positionthe reader head of the reader covers the first track and the secondtrack.
 11. The storage device of claim 10, wherein: the pre-determinedposition comprises one of a pre-determined position on the first trackor a pre-determined position on the second track.
 12. The storage deviceof claim 10, wherein: the first track is adjacent to the second track.13. The storage device of claim 9, wherein: the reader is furtherconfigured to read a plurality of signals, wherein for each signal thereader head of the reader is at a different position of the storagemedium; and the determination circuit is further configured to determinedata stored at the predetermined position of the storage medium based onthe plurality of signals.
 14. The storage device of claim 9, wherein:the reader is further configured to read a frequency burst signal withthe reader head of the reader at a position of the storage mediumcomprising a frequency burst provided before a data track on the storagemedium; and the determination circuit is further configured to determinethe data stored at the pre-determined position of the storage mediumfurther based on the frequency burst signal.
 15. The storage device ofclaim 9, wherein: the storage medium comprises a plurality of trackshaving a width smaller than a width of the reader head of the reader;and the storage medium comprises at least one track having a width equalto or larger than the width of the reader head of the reader.
 16. Thestorage device of claim 9, wherein: the determination circuit is furtherconfigured to determine the data stored at the pre-determined positionof the storage medium further based on determining a phase offset ofdata stored at the second position of the storage medium.